1. Field of the Invention
This invention relates generally to an inductor array for a boost converter and, more particularly, to an inductor array for a boost converter that includes a plurality of inductors where adjacent inductors have a shared core piece to provide a shared flux path.
2. Discussion of the Related Art
Hydrogen is a very attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. A hydrogen fuel cell is an electro-chemical device that includes an anode and a cathode with an electrolyte therebetween. The anode receives hydrogen gas and the cathode receives oxygen or air. The hydrogen gas is dissociated in the anode to generate free hydrogen protons and electrons. The hydrogen protons pass through the electrolyte to the cathode. The hydrogen protons react with the oxygen and the electrons in the cathode to generate water. The electrons from the anode cannot pass through the electrolyte, and thus are directed through a load to perform work before being sent to the cathode.
Proton exchange membrane fuel cells (PEMFC) are a popular fuel cell for vehicles. The PEMFC generally includes a solid polymer electrolyte proton conducting membrane, such as a perfluorosulfonic acid membrane. The anode and cathode typically include finely divided catalytic particles, usually platinum (Pt), supported on carbon particles and mixed with an ionomer. The catalytic mixture is deposited on opposing sides of the membrane. The combination of the anode catalytic mixture, the cathode catalytic mixture and the membrane define a membrane electrode assembly (MEA). MEAs are relatively expensive to manufacture and require certain conditions for effective operation.
Several fuel cells are typically combined in a fuel cell stack to generate the desired power. For example, a typical fuel cell stack for a vehicle may have two hundred or more stacked fuel cells. The fuel cell stack receives a cathode input gas, typically a flow of air forced through the stack by a compressor. Not all of the oxygen is consumed by the stack and some of the air is output as a cathode exhaust gas that may include water as a stack by-product. The fuel cell stack also receives an anode hydrogen input gas that flows into the anode side of the stack.
The fuel cell stack includes a series of bipolar plates positioned between the several MEAs in the stack, where the bipolar plates and the MEAs are positioned between two end plates. The bipolar plates include an anode side and a cathode side for adjacent fuel cells in the stack. Anode gas flow channels are provided on the anode side of the bipolar plates that allow the anode reactant gas to flow to the respective MEA. Cathode gas flow channels are provided on the cathode side of the bipolar plates that allow the cathode reactant gas to flow to the respective MEA. One end plate includes anode gas flow channels, and the other end plate includes cathode gas flow channels. The bipolar plates and end plates are made of a conductive material, such as stainless steel or a conductive composite. The end plates conduct the electricity generated by the fuel cells out of the stack.
Most fuel cell vehicles are hybrid vehicles that employ a supplemental power source or rechargeable electrical energy storage device (RESS) in addition to the fuel cell stack, such as a high voltage DC battery, a super-capacitor or an ultracapacitor. The RESS provides supplemental power for the various vehicle auxiliary loads, for system start-up and during high power demands when the fuel cell stack is unable to provide the desired power. The fuel cell stack provides power to an electric traction motor through a DC high voltage bus line for vehicle operation. The RESS provides supplemental power to the voltage bus line during those times when additional power is needed beyond what the stack can provide, such as during heavy acceleration. For example, the fuel cell stack may provide 70 kW of power. However, vehicle acceleration may require 100 kW of power. The fuel cell stack is used to recharge RESS at those times when the fuel cell stack is able to provide the system power demand. The generator power available from the traction motor during regenerative braking is also used to recharge the RESS.
In the hybrid vehicle discussed above, a boost DC/DC converter is sometimes employed to match the lower voltage fuel cell stack to the higher voltage RESS. DC/DC converters often employ a multi-phase array of inductors that provide the task of increasing the DC voltage. A typical inductor in the inductor array includes a magnetic core, such as an iron core, where a gap is provided between core pieces. Isolated metal windings are wrapped around the core as a coil and a current propagating through the windings generates a magnetic flux in the core and the gap. Suitable switching is provided to switch the voltage applied to the windings so that the magnetic flux change increases the voltage potential at the output of the converter.
There has been an effort in the industry to reduce the size, weight and cost of DC/DC converters in fuel cell systems for vehicles, and increase their reliability and efficiency.